In the conventional authentication apparatus such as an electronic lock, a key manufacturer determines an authentication data in advance, and completes and sells, as a set, a key body (or a lock) and a key to be inserted into the key body. The user purchases the complete product and uses by mounting it on the front door, for example, at a required point. In electronic locks of other types, the time when the lock has been shut is stored in the key body and the key as authentication data, which is collated at the time of opening the lock (Japanese Patent Application Laid-open No. H07-233663), or a voiceprint (or a voice pattern) is used as authentication data (for example, Japanese Patent Application Laid-open No. H08-257216).